With rapid developments in communications, computer networks and semiconductor technologies, a variety of services are provided using wireless communication networks. Not only that, users are requiring higher-level services and wireless internet service market around the world is growing explosively. To accommodate these trends, a mobile communication system using a wireless communication network is being evolved to provide a multimedia communication service transmitting various data in addition to a voice service.
Recently, wireless data services through code division multiple access (CDMA) 2000, evolution data only (EV-DO), wideband CDMA (WCDMA) and wireless local area networks (WLANs) have been commercialized. Thus, the residential use of mobile phones and the demand for mobile data at home have increased steadily. To keep up with such trend, a method for providing mobile communication services by installing a small cell base station indoors has been proposed so as to access a core network of the mobile communication system through an indoor broadband network. Particularly in a next-generation network system, a method of disposing a number of small size cells (e.g., femto-cells) has been proposed to meet the demand for a high data transmission rate and facilitate stable and reliable providing of various services. A small cell base station covering such small size cells may otherwise be referred to as an indoor base station or a femto base station and a Home-eNB, a HeNB or the like in the 3rd Generation Partnership Project (3GPP). As such, by reducing the size of the cell to be served in an indoor environment, efficiency of the next-generation network system using a high frequency band can be improved. Further, using a number of small size cells is advantageous in that the number of times of frequency reuse can be increased. Also, such a small size multiple cell using scheme offers an advantage of improving the deteriorated channel status due to radio wave attenuation which is caused by controlling the entire cell area with only one base station. The scheme also offers the advantage of enabling services to a user in a shadow area, which used to be impossible. Based on these advantages, a scheme of combining a conventional macro-cell (a cell area controlled by an outdoor base station) and a femto-cell (a cell area controlled by a small cell base station such as an indoor base station, a femto base station and the like) is newly devised and is drawing attention.
The above-described cell combining scheme has advantage in light of the provision of service. Such a scheme, however, has disadvantage in that it requires a larger number of base stations to provide high quality data service in the same area to thereby increase costs in installation and operation of the base stations. In particular, a lot of labor and time are required to determine a parameter in relation with radio or cable characteristics. Further, merely with a centralized management, it is difficult to efficiently cope with constant environmental changes. Furthermore, when changes are made, a redefinition with respect to the whole system should be given. Thus, it is not easy to detect optimum conditions with respect to a variable location of the base station (that is, the small cell base station is installed by a user where he/she wants, not at the optimum location designated by a service provider) and constantly changing wireless environments. These circumstances necessitate devising a self-organizing network (SON) designed to adapt to the wireless environments, where the base stations and networks are randomly installed and also automatically change, and data traffic environments. For implementation of the SON, measurement of wireless information and surrounding network information are needed. Accurate and abundant input information facilitates implementation of effective SON algorithm.
Ordinarily, installation of a base station accompanies the following procedures: to obtain the location of the base station, estimate radio wave propagation environments, then predict neighbor cells to which a user equipment can perform a handover, and thereby make a neighbor cell list (NCL). The NCL broadcasted by the base station refers to information which indicates configurations of the neighbor cells when the user equipment serviced by the serving base station performs the handover to one of the neighbor cells. The base station broadcasts the NCL and the user equipment to perform the handover to another cell performs neighbor cell search by using the broadcasted NCL.
As described above, to cope with the mobile communications market trend that requires small cell coverage, a larger number of base stations are necessary to provide high quality data services in the same area. Installation and maintenance of a large number of base stations entails enormous costs for network installation and maintenance. Under these conditions, it is difficult to manually set an NCL every time in installing a base station, in terms of management and operation. Furthermore, in small cell base stations such as indoor base stations and femto base stations, it is expected to install larger number of the base stations, and it is required to allow the on/off of the base stations to become free and secure the mobility of the base stations. Therefore, in manually configuring an NCL, there is a difficulty in network management as well as cost.
Accordingly, when a base station is installed indoors or outdoors, the function of SON that allows the base station to autonomously access or set a network and appropriately performs cell optimization and management according to an ambient wireless environment is acutely required. A network provider can automatically manage and operate a manually controlled network over the SON.